Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $229.62   11.606%   $256.2697   $256.27   $256.25   $256.30  
  Purchase #2 $73.48   12.272%   $82.4975   $82.50   $82.50   $82.50  
  Purchase #3 $236.88   6.336%   $251.8887   $251.89   $251.90   $251.90  
  Purchase #4 $118.26   3.649%   $122.5753   $122.58   $122.60   $122.60  
  Purchase #5 $129.59   11.454%   $144.4332   $144.43   $144.45   $144.40  
  Purchase #6 $248.85   5.251%   $261.9171   $261.92   $261.90   $261.90  
  Purchase #7 $110.55   3.331%   $114.2324   $114.23   $114.25   $114.20  
  7 purchase totals = $1,147.23       $1,233.8139   $1,233.82   $1,233.85   $1,233.80